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The objective was to study the effect of serious psychiatric disorders on participation in a general health population study. This was done by linking the records of the Second Tromsø Health Study to the case register of a mental hospital. The participants in the Second Tromsø Health Study were 21,441 persons, the total population of men aged 20-54 and women aged 20-49 years who resided in Tromsø, Norway, in 1979. The authors found that both men and women with psychiatric illness had approximately 20% lower attendance rates. Nonattenders to the survey had 2.5 times higher prevalence of psychiatric disorders than did attenders of both sexes. Age, marital status, and various psychiatric diagnoses were all significant predictors of nonattendance. Nonattendance led to underestimation of the prevalence of psychiatric disorders in the population. The conclusion is that in general health studies, even those with high attendance rates, the estimates of prevalence of psychiatric disorders in the population are seriously affected by nonattendance. Prevalence ratios between groups of the population were not much affected by nonattendance.
Vidje Hansen (Thu,) studied this question.